President Obama is hitting the campaign trail Tuesday, traveling to New York City to kick off a full plate of political events this week on behalf of his Democratic allies. The president will be at a fundraiser for a congressional candidate from upstate New York, and then he'll attend another fundraiser for the Democratic National Committee that is expected to generate between $2 million and $3 million. 

The president will squeeze in some official duties on the side -- in this case, a tour of the Joint Terrorism Task Force headquarters followed by a speech to staff members. Under White House travel rules, official business on such excursions allows the administration to write off a big part of the trip at taxpayer expense. Previous administrations, including those of George W. Bush and Bill Clinton, also helped defray political expenses in this way. 

Travel rules developed under the Reagan administration state that the Air Force pays all costs for the use of the aircraft on such trips, but that the government must be reimbursed for airfare, food, lodging and other expenses incurred during whatever portion of the trip is political. 

But reimbursement for political activities involves a tricky formula, and actual reimbursements typically come nowhere close to compensating the government for the cost of such trips. 

Secret Service costs, for one, are always footed by the government. A 2006 report for the House Committee on Oversight and Government Reform found that during 2002, political campaigns reimbursed the federal government for $198,000 of the $6.5 million in flight expenses racked up by campaign-related stops made by President Bush and Vice President Dick Cheney

Obama's political schedule this week is particularly aggressive. 

By week's end, he will go to a rally for New Jersey Gov. Jon Corzine, who is trying to fend off Republican challenger Chris Christie in a very close race; he'll visit Boston to raise money for Massachusetts Gov. Deval Patrick, who is up for  re-election in 2010; and he'll travel to a Connecticut fundraiser for Sen. Chris Dodd, who is seeking another term next year. In one week, Obama will campaign for Democrat R. Creigh Deeds, who trails Republican Bob McDonnell in the race for Virginia governor. 

Obama, who remains highly popular within his party and serves as the Democrats' best fundraiser, plans a final burst on behalf of candidates right before the Nov. 3 election. 

Most eyes are on the hard-fought elections in Virginia and New Jersey, the only two gubernatorial races in the country this year. In New York, Democrat Bill Owens is running in a special election to represent the sprawling, rural 23rd district that has had no representative since Republican Rep. John McHugh resigned to become secretary of the Army under Obama. 

Already looming are next year's midterms. Democrats need to stockpile a ton of cash as they seek to defend their majorities in both houses of Congress and to pick up governors' seats next November. The party in power typically loses seats in the midterm election of a president's first term. 

Republicans have taken notice, and they are taking aim at Obama's plans this week. The Republican Study Committee, a caucus of House conservatives, juxtaposed Obama's schedule with a request from the top commander in Afghanistan for more U.S. troops; Obama is conducting a war strategy review before deciding on troop levels. 

"The clock is ticking in Afghanistan," the Republican committee said Monday. "Hopefully the president can still hear it over the ringing of the cash register." 

The Associated Press contributed to this report.